The invention relates to a process for preparing 6,6′-((3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyl)bis(oxy))bis(2,4,8,10-tetramethyldibenzo[d,f][1,3,2]dioxaphosphepine).
Phosphorus-containing compounds, as ligands, play a crucial role in a multitude of reactions. Said compounds include phosphite ligands, i.e., compounds comprising P—O bonds, used in hydrogenation, hydrocyanation and especially hydroformylation.
The reactions between olefin compounds, carbon monoxide and hydrogen in the presence of a catalyst to give the aldehydes comprising one additional carbon atom are known as hydroformylation or oxo synthesis. These reactions often employ compounds of the group VIII transition metals as catalyst. Known ligands include, for example, compounds of the phosphine, phosphite and phosphonite classes each comprising trivalent phosphorus PIII. A good overview of the state of the art in the field of olefin hydroformylation may be found in B. CORNILS, W. A. HERRMANN, “Applied Homogeneous Catalysis with Organometallic Compounds”, vol. 1 & 2, VCH, Weinheim, N.Y., 1996 or R. Franke, D. Selent, A. Börner, “Applied Hydroformylation”, Chem. Rev., 2012, DOI:10.1021/cr3001803.
The synthesis of symmetric bisphosphites is conventionally known as described in U.S. Pat. No. 4,769,498 for example, and the use thereof in catalytically active transition metal-containing compositions for the hydroformylation of unsaturated compounds.
U.S. Pat. No. 4,769,498 and also U.S. Pat. No. 5,723,641 describe the preparation of preferably symmetric bisphosphites and the use thereof as ligands for hydroformylation. The symmetric bisphosphite ligands used in the hydroformylation are prepared at low temperatures. Adherence to these low temperatures is absolutely necessary since according to the description of these documents higher temperatures would lead to unwanted rearrangements and ultimately to asymmetric bisphosphites.
When symmetric bisphosphites are employed as ligands in transition metal-catalysed hydroformylation they generally exhibit distinctly higher reactivities and improved n-regioselectivity (see Rhodium-catalyzed Hydroformylation, ed. by P. W. N. M. van Leeuwen and C. Claver, Kluwer Academic Publishers 2006, AA Dordrecht, NL, pages 45-46).
Synthetic routes to symmetric ligands are conventionally known. However, said routes generally give mixtures of symmetric and asymmetric ligands. Small quantities of these mixtures are separable using appropriate column chromatography processes for example. However, these separation processes are impracticable for larger quantities of product or for use on a large industrial scale.
Direct preparation of pure 6,6′-((3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyl)bis(oxy))bis(2,4,8,10-tetramethyldibenzo[d,f][1,3,2]dioxaphosphepine) (I) has hitherto been unsuccessful since transesterification to generate asymmetric 4,8-di-tert-butyl-2,10-dimethoxy-6-((3,3′,5,5′-tetramethyl-2′-(2,4,8,10-tetramethyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy)-[1,1′-biphenyl]-2-yl)oxy)dibenzo[d,f][1,3,2]dioxaphosphepine (II) takes place during the reaction.
It is an object of the present invention to provide a process whereby the compound 6,6′-((3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyl)bis(oxy))bis(2,4,8,10-tetramethyldibenzo[d,f][1,3,2]dioxaphosphepine) (I) is obtained. Additionally, the proportion of 4,8-di-tert-butyl-2,10-dimethoxy-6-((3,3′,5,5′-tetramethyl-2′-((2,4,8,10-tetramethyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy)-[1,1′-biphenyl]-2-yl)oxy)dibenzo[d,f][1,3,2]dioxaphosphepine (II) in the end product should also be very low.
It should preferably be possible to use the process on a large industrial scale. Processes unrealizable in large scale manufacture, such as separation by column chromatography for example, should therefore be eschewed.